Achieving future fuel efficiency improvements in medium and heavy duty commercial trucks and buses will be a challenging task for commercial truck and diesel engine manufacturers. Over the past several decades, fuel efficiency improvements have been realized largely through the application of computer technology to the design and development of engines and powertrains and through the adoption of sophisticated engine control systems in commercial trucks. Hybrid powertrains have contributed to fuel economy improvements, but at significantly increased manufacturing costs that raise prices that purchasers must pay. The inventor believes that further improvements in conventional single-engine/powertrain design and development and in engine control systems are unlikely to yield more than minimal fuel economy improvements.
Currently manufactured long haul commercial trucks commonly use large diesel engines in the range of 400-600 maximum horsepower as their prime movers. An engine having such a maximum power output is necessary to accommodate the peak power requirement for typical vocation drive cycles of those vehicles.
The current cost of hybrid powertrains does not justify their wide-spread adoption by the commercial trucking industry. Current sales of hybrid truck, buses, and coaches are predominantly in fulfillment of governmental contracts which use taxpayer funds as a subsidy for the additional costs of such “green” technologies in purchased vehicles.
Current large displacement fixed horsepower diesel engines operate within sub-optimal efficiencies, commonly within ranges between 800 and 2200 revolutions per minute (RPM). Because they accommodate changes in torque and power demand by varying engine RPM, such engines are inherently incapable of achieving optimum performance and best fuel economy.
Failure of a current diesel engine while a vehicle is on the road may create a hazardous condition for the driver and surrounding traffic and/or disable the vehicle to such an extent that unexpected delay, economic losses, and/or customer dissatisfaction become inevitable results of the failure.
Virtually all commercial trucks, buses and coaches on the roads today use conventional brake pads exclusively to decelerate the vehicle, converting the kinetic energy into wasteful heat. While such waste can be partially mitigated by a hybrid powertrain, hybrid powertrains are, as mentioned earlier, not currently cost-justifiable. A hybrid powertrain also inherently adds weight to a vehicle, a fact that adversely impacts fuel economy.
The inventor's U.S. Patent Publication No. 2012 0152631 discloses a drive which when used to propel a vehicle, especially a large commercial vehicle such as a truck or bus for example, selectively uses one or both of two internal combustion engines, especially turbocharged diesel engines, depending on torque and power demands being imposed on the vehicle as it is being driven. The inventor's analysis of that drive shows that this selective use of the engines can enable a vehicle to achieve significant fuel economy improvements in comparison to improvement which is likely to be obtained in engines and engine controls through use of conventional single-engine/powertrain design and development techniques which were mentioned earlier.
The inventor's analysis shows that a single one of two V8 engines can provide sufficient power and torque for approximately 80% of a typical long haul drive cycle. During portions of a drive cycle where demand is greater, such as climbing a grade or accelerating the vehicle, a controller automatically starts a second V8 engine to provide the additional power required. Once the drive cycle returns to lesser demand, the controller automatically turns off one of the engines. In this way the invented drive is capable of maximizing efficiency through optimized variable power delivery.
Each of the two engines is more compact than a single large engine which is capable of delivering maximum power comparable to that of the drive disclosed in when both of its engines are operating the invented drive at maximum power.
Failure of one of the two engines while the vehicle is on the road is unlikely to disable the vehicle because the other engine can be used in most driving situations to drive the vehicle directly to a service facility or to a suitable off-road location.
The drive disclosed in U.S. Patent Publication No. 2012 0152631 can recover substantial brake energy by charging an on-board energy storage system, examples of which are electric energy storage in a battery, battery bank, or ultra-capacitor and hydraulic energy storage in an accumulator. Refuse collection and package delivery vocations present perhaps the largest market opportunity for energy recapture due to low average speeds with frequent stop and start driving. Line haul vocations offer less opportunity for brake energy recapture due to continuous, high speed, non-start-and-stop drive cycles.
An example of the dual-engine, variable-power drive disclosed in U.S. Patent Publication No. 2012 0152631 comprises two generic V8 diesel engines having opposite flywheel rotation which can operate concurrently to deliver power through one or more drive axles to driven wheels that propel a wheeled vehicle such as a commercial truck. When both engines are running at the same power output level, engine torque reaction is cancelled through the respective engine mountings. The SAE (Society of Automotive Engineers) standard diesel engine has counter-clockwise flywheel rotation. The inventor is unaware of any electric generator, other than one embodiment disclosed in his U.S. Patent Publication No. 2012 0152631, which can accommodate counter-clockwise mechanical rotation energy of two standard diesel engines. In that embodiment the engines do not rotate about a common axis.
Although the inventor's publication discloses another embodiment which also uses two diesel engines, one at each end, rotating about a common axis, such a configuration requires one engine to rotate in the clockwise direction and the other in the counterclockwise direction. Clockwise rotation diesel engines are not commonly manufactured. Although such an engine could be manufactured, it would be a special order low volume product that would significantly increase the total cost of manufacturing and maintenance for the two-engine, single-generator configuration.